采用复合单元法模拟裂隙多孔介质变饱和流动

采用复合单元法建立了模拟裂隙多孔介质变饱和流动的数值模型。该模型具有以下特点:裂隙不需要离散成特定单元,而是根据几何位置插入到孔隙基质单元中形成复合单元;在复合单元中,分别建立裂隙流和孔隙基质流的计算方程,二者通过裂隙-基质界面产生联系并整合成复合单元方程;复合单元方程具有和常规有限单元方程相同的格式,因此,可以使用常规有限单元方程的求解技术。采用欠松弛迭代、集中质量矩阵以及自适应时步调节等技术,开发了裂隙多孔介质变饱和流动计算程序。通过模拟一维干土入渗和复杂裂隙含水层内的流动问题,验证了该模型的合理性和适用性。模拟结果为进一步认识非饱和裂隙含水层地下水流动特性提供了理论依据。

Simulation of variably-saturated flow in fractured porous media using composite element method

A numerical model for simulating variably-saturated flow in fractured porous media is established using the composite element method. The model has the following features. The fractures do not need to be discretized into specific elements, but are inserted into the porous matrix elements according to their geometric positions to form the composite elements. Within the composite element, the calculation equations for the fracture flow and the porous matrix flow are built respectively, which can be linked by the fracture-matrix interface and integrated into the composite element equation. The composite element equation has the same format as the conventional finite element equation, so the solving techniques for the conventional finite element equation can be applied to the composite element one. Using the techniques of under-relaxation iteration, mass matrix lumping and adaptive time-stepping, a calculation program for variably-saturated flow in fractured porous media is developed. The rationality and applicability of the model are verified by simulating the one-dimensional infiltration into dry soils and the flow in complex fractured aquifers. The simulation results provide a theoretical basis for further understanding groundwater flow characteristics in unsaturated fractured aquifers.